This invention relates to catheters and intraluminal delivery devices.
There are many devices used to treat vascular diseases which require introduction of catheters and catheter based devices into the blood vessels. Blockages of the coronary arteries and peripheral arteries such as the femoral artery, iliac artery, and carotid artery can be treated or cured by placement of stents which keep arteries open. Blockages can also be cured, at least temporarily, with angioplasty balloons, atherectomy devices, endarterectomy devices, and embolectomy devices. Aneurysms of the aorta, femoral artery, carotid artery and other arteries can be treated with the placement of stent grafts into the artery which isolate the aneurysm from the blood stream. Placement of these devices is accomplished percutaneously by inserting the catheter into a remote peripheral blood vessel such as the femoral artery in the groin (the femoral, carotid, or subclavian arteries are frequently used), and then snaking the tip of the catheter to the diseased portion of the artery. For example, a catheter can be placed into the coronary arteries through a circuitous route from the femoral artery, up the aorta, over the aortic arch, and turning into any of the coronary arteries which communicate with the aorta. Likewise, a graft may be placed in the aorta through a percutaneous puncture in the femoral artery in the thigh or the carotid artery in the neck. Catheter based stents, probes, etc. may be used in other tortuous body lumens such as the urethra, ureter, biliary ducts, and fallopian tubes.
Many diagnostic and device deployment catheters have sharp or irregular contours which can damage the inside wall of blood vessels when the devices pass through the blood vessel and scrape the sides of the blood vessel. For example, stents used for coronary arteries are typically expanded metal stents mounted on balloon catheters, with the stent surrounding the balloon, and the balloon tightly compacted within the stent. The outer contours of these balloon mounted stents can be quite sharp and irregular, and damage caused to the inside wall of blood vessels is common. The damage caused to blood vessels during stent deployment can lead to further occlusion of the vessel as the blood vessel heals.
The placement of stents, ultrasound imaging catheters, angioplasty balloon, angiography contrast medium injection catheters and the like generally requires (1) percutaneous puncture of a large artery such as the femoral artery with a large needle (2) insertion of an introducer sheath through the puncture, (3) insertion of a guidewire through the introducer sheath into the artery (4) steering the guidewire through the vasculature until it is near, or slightly past, the diseased portion of a blood vessel and (5) mounting a diagnostic catheter or treatment catheter on the guidewire and pushing the catheter along the guidewire until it reaches the diseased portion of the blood vessel. For some applications, additional sheaths may be used, such as the doogie sometimes used to prevent the hemostasis valve from dislodging or damaging the stent during insertion. Each of these introductions involves passage of blunt or irregular objects along the inner surface of blood vessels, which can cause damage to the intima or inner wall of the blood vessels.
The problem of intimal damage is especially apparent in stent deployment catheters. Stents are commercially available in several forms, and many others have been proposed in patents and the medical literature. The Palmaz(trademark) stent is a expandable metal stent mounted on an angioplasty balloon (the stent is sometimes sold separately from the angioplasty balloon). The Palmaz-Schatz(trademark) stent is similar to the Palmaz(trademark) stent, with several stent sections linked together. These stents are often used to treat stenosis and blockage of the coronary arteries. The stent proposed by Beck, Device for the Widening of Blood Vessels, U.S. Pat. No. 4,877,930 (Oct. 31, 1989) is made of a rolled frame mounted on a balloon, with exposed sharp edges. Wiktor, Intracoronary Stent and Method of Simultaneous Angioplasty and Stent Implant, U.S. Pat. No. 4,969,458 (Nov. 13, 1990) shows a xe2x80x9cnotebook bindingxe2x80x9d type wire stent mounted on a balloon, with exposed irregular surfaces. Very similar structure is disclosed in Gianturco, Endovascular Stent and Delivery Method, U.S. Pat. No. 5,041,126, (Aug. 20, 1991). Hillstead, Apparatus and Method for Placement of a Stent within a subject vessel, U.S. Pat. No. 5,019,085 (May 28, 1991) shows a self expanding wire stent mounted on a balloon. Sinofsky, Endovascular Stent and Delivery System, U.S. Pat. No. 5,100,429 (Mar. 31, 1991) shows a rolled stent mounted on a balloon. The Craggstent(trademark), the Wallstent(trademark), and various other commercially available stents also have sharp and irregular surfaces which come into contact with the inner surface of blood vessels during placement. Other environments are also suitable for stent use. For example, the Urolume(trademark) braided urethral stent (American Medical Systems) and the Titan(trademark) titanium tube stent (Boston Scientific) are intended for use in the urethra, and they are visibly sharp-edged stents which must be carefully placed in the urethra to avoid unwanted injury.
A fairly common problem with stent deployment is slippage and early unintentional release of the stent. The stent may pop off the balloon during inflation, or slip backward off the balloon during steering to the intended site of release. Additionally, passage of the exposed stent through the hemostasis valve causes the stent to be dislodged from the balloon. Self-expanding stents are particularly difficult to release in the desired position because they start to expand as soon as the sheath or wires used to retain them are removed. Self-expanding and balloon expanding stents may have to be withdrawn from the blood vessel, backward (proximally) into the delivery sheath, if the stent is misplaced or improperly expanded. After a stent slips backward of the balloon, or if it slips forward off the balloon in a partially expanded condition, the steps necessary to remove the stent can severely damage an artery, and may even require grossly invasive surgery to remove the stent. It has been proposed by Euteneuer, et al., Single Layer Hydraulic Sheath Stent Delivery Apparatus and Method, U.S. Pat. No. 5,445,646 (Aug. 29, 1995) to use several bands of dissolvable material to control the release of a self expanding stent. The bands proposed by Euteneuer are used in conjunction with a sheath which acts as a fairing surface and adds significantly to the outer diameter of the device. The bands themselves add significantly to the outer diameter of the stent assembly and leave exposed sharp and irregular contours of the stent.
To solve the problems described above and alleviate the potential damage of catheter deployed devices such as stents to the inner wall of blood vessels and other body lumens, the distal end of the catheter, including the irregularly shaped stent, or at least some portion of the stent, is coated with a bioabsorbable and quickly dissolvable (but not too quickly) material. The bioabsorbable material encapsulates the catheter deployed device, providing a smooth autraumatic surface for the device during passage through the vasculature. When used in a stent catheter, the material serves as an adhesive or structural locking mechanism to keep the stent securely attached to the catheter during insertion and expansion. The material dissolves in blood or water, and within a few minutes is completely dissolved away from the device, leaving the device ready for use or placement within the body. The material optimally takes several minutes to dissolve, allowing the surgeon placing the device a reasonable amount of time to snake the device into place. The preferred material is a polysaccharide such as mannitol, sorbitol, sucrose, xylitol, anionic hydrated polysaccharides such as gellan, curdlan, XM-6, xanthan.